The present invention relates to an anti-contamination coating composition used for surface finishing of various materials such as metal, glass, porcelain tile, concrete, sideboard, extrusion-molded plate, plastic and the like. More particularly, it relates to an anti-contamination coating composition used for coating finishing of structures such as building structures, bridges and the like, which can also be coated directly on a substrate and can also be used in a coating composition used as a final finishing coating such as various finishing coatings, pattern coating, coating for forming the stone-like surface, coating for forming the patterned surface or the like.
Coating finishing has hitherto been performed to protect a substrate of building structures, or civil engineering structures, and to impart design and to improve the appearance. However, a large amount of oily contaminants have recently been floating in the air as a result of an exhaust gas discharged from automobiles in the center of the city and suburbs thereof. When those oily contaminants adhere to the surface of the coat formed by using a high-durability coating, a considerable sooty or striped contamination (hereinafter referred to as xe2x80x9crain-striped contaminationxe2x80x9d) occurs, therefore, the coating finishing provided to improve the scene of the city was meaningless sometimes.
Japanese Patent Kokai Publication No. 4-370176 discloses a coating comprising a segmented polymer containing a hydrophilic segment such as polyalkylene oxide segment and a hydrophobic segment such as polysiloxane. This coating is capable of obtaining such an effect that water derived from rainfall penetrates/flows into the interface between the coat and contaminants to wash off contaminants together with water (soil release effect) by imparting the hydrophilicity to the coat surface. Although the hydrophilicity is imparted when water is present on the coat surface, the hydrophobicity is actually imparted when the coat surface has no opportunity to contact with water for a long period of time. Therefore, there is a problem that it takes a considerably long time to convert the hydrophobicity of the coat surface into the hydrophilicity during rainfall , so that the contamination during rainfall can not be prevented.
Japanese Patent Application No. 6-506632 (International Publication WO94/06870) discloses an anti-contamination coating composition wherein organosilicate is added in the coating and the coat surface is hydrophilized by the reaction thereof and, furthermore, a soil release effect is utilized. The organosilicate forms a silanol group or a siloxane bond by the hydrolysis reaction in the presence of an acid catalyst, and this silanol group or siloxane bond imparts the hydrophilicity to the coat surface. Taking actual coating on the outside wall of buildings into consideration, the reaction may proceed by acidic rain, but it takes a considerably long period of time after formation of the coat to obtain the hydrophilic surface enough to sufficiently exert the soil release effect, similar to the above technique.
Japanese Patent Kokai Publication No. 6-145453 discloses a method of mixing an acrylic silicone resin with organosilicate to obtain a hydrophilic coat. According to this technique, a large amount of organosilicate is required to impart sufficient hydrophilicity to the coat. However, when a large amount of organosilicate is added, the crosslink density of the coat becomes too large and the coat becomes brittle. At the same time, a large amount of siloxane bonds are introduced to cause deterioration of the chemical resistance of the coat, which results in deterioration of the weathering resistance of the coat as contradiction.
In such a way, among coats formed by using conventional anti-contamination coating, those requiring a long period of time to hydrophilize the surface can cause rain-striped contamination within a very short period of time after application of the coating.
Originally, the anti-contamination coating has the effect of causing no contamination, and users and builders who request the coating expect that effect. Accordingly, the fact that contamination arises even at the initial stage after formation of the coat fails to meet the expectation of these users and builder temporarily, and the fact also imparts a sense of unease to the anti-contamination effect for a long period of time. Since a conventional anti-contamination coating has a main object of washing out contaminants by rainfall, the anti-contamination coating is inferior in stain resistance of once adhered contamination. It has been found that, when there is no rainfall for a long period of time, oily contamination penetrates into the coat to cause contamination which is hardly washed out by rainfall no longer.
An object to be solved by the present invention is to obtain an anti-contamination coating composition for providing an anti-contamination coat, which has a soil release effect of washing out contaminants because the surface exerts the hydrophilicity immediately after formation of the coat, not showing hydrophilicity by an action formed after formation of the coat, such as waterfall, and which is strong but not brittle because of its specific crosslinked structure, and has excellent stain resistance to oily contamination, good weathering resistance and good coat physical properties.
Another object to be solved by the present invention is to provide a coating composition which can improve the interlaminar adhesion (hereinafter referred to as a xe2x80x9crecoating propertyxe2x80x9d) when multi-layer coating is performed on a topcoat layer after curing an undercoat layer using a reaction curing type polyurethane or polyurethane-acrylic anti-contamination coating, and effectively prevent blister, crack or lifting (a phenomenon wherein shrinkage occurs on the coat surface as a result of dissolution of the uncured portion of the undercoat layer by a solvent of the coating of the topcoat layer because of insufficient curing and adhesion of the coat of the undercoat layer in case of multiple coating) caused with a lapse of time.
Such an anti-contamination high-durability coating is exclusively a solution type of an organic solvent. With recent enhancement of the environmental awareness, there have been used those using as weak a solvent as possible. Furthermore, it has been required to convert into an aqueous coating.
It is generally considered that, when organosilicate (i.e. alkyl silicate) is added in the coating, it reacts with water in the air during the formation of the coat, and an alkoxysilyl group Sixe2x80x94OR is converted into a silanol group Sixe2x80x94OH and alkyl silicates having a silanol group are arranged on the coat surface, thereby exhibiting the hydrophilicity.
It is assumed that, when using a resin which is only dissolved in a solvent having high dissolving power, since the coat is certainly hydrophilic and the anti-contamination effect can also be obtained, such a surface orientation occurs. When using a urethane resin using a polyol having a solubility parameter of about 6.5 to 9.5, which is also dissolved or dispersed in a solvent having low dissolving power, there arise white turbidity of a film and such phenomenon that the anti-contamination is not obtained. Therefore, there is much room for improvement.
A finishing coating material whose main material layer has rubber elasticity referred to as a waterproofing multi-layer coating material, which is used in coating finishing performed in the case of a substrate of building structures, civil engineering structures, etc., has been noted and widely used because it has a follow-up property to crazing (hereinafter referred to as xe2x80x9ccrackxe2x80x9d) of the outside wall of concrete and an effect for inhibition of penetration of a carbon dioxide gas.
This waterproofing multi-layer coating material is composed of an undercoat layer, a main material (a continuous layer and a patterned layer, which have rubber elasticity) and a topcoat material, but the topcoat layer is coated with an elastic coating following the main material layer. When coating finishing is performed on the whole outside wall including the butt portion (joint portion) between boards joined by using a sealing material in a dry technique using a dry building material represented by sideboard, extruded plate, etc., an elastic coating capable of following movement of the sealing material driven portion is used. Furthermore, an elastic coating is often used to a raw material such as metal, wherein degree of expansion and shrinkage is comparatively large, and to a substrate whose structural movement is assumed.
However, there is a problem in that the coat obtained from these elastic coatings is generally inferior in resistance to surface contamination to a rigid coat.
Under these circumstances, the present inventors have found that, by mixing a hydrophilic alkoxysilane compound containing an alkylene oxide chain with an acrylic silicone resin and an alkyl silicate (organosilicate), as described in Japanese Patent Kokai Publication No. 9-31401, hydrophilization is exhibited from the comparatively initial stage in the coat surface to be formed from the composition. However, there was much room for improvement in anti-contamination performance immediately after formation of the coat.
The alkyl silicate (organosilicate) used in a conventional anti-contamination coating is closely related to brittleness of the formed coat, depending on the amount and combination with the kind of the used resin. Therefore, there is a fear of causing crack in the coat. Furthermore, the alkyl silicate (organosilicate) is very expensive as a raw material for coating and, therefore, it was a large problem to coating makers in view of the raw material cost.
That is, the problems to be solved by the present invention are as follows.
(i) To obtain an anti-contamination coating composition for providing an anti-contamination coat, which has a soil release effect of washing out contaminants because the surface exerts the hydrophilicity immediately after formation of the coat, not showing hydrophilicity by an action formed after formation of the coat, such as rainfall, etc., and has excellent stain resistance to oily contamination, good weathering resistance and good coat physical properties.
(ii) To provide a coating composition, which can improve the interlaminar adhesion (hereinafter referred to as a xe2x80x9crecoating propertyxe2x80x9d) when multi-layer coating is performed, and effectively prevent blister, crack or lifting caused with a lapse of time.
(iii) To provide a coating composition, which has characteristics of the above items (i) and (ii), and can use a weak solvent which hardly causes environmental problems.
(iv) To provide a coating composition, which has characteristics of the above items (i) and (ii), and forms an elastic coat which hardly causes crazing with a lapse of time.
(v) To provide a coating composition, which exerts the same effect even if the amount of an expensive silicate compound mixed becomes lower in order to exhibit excellent soil-release effect immediately after formation of the coat, and also contributes to reduce the cost.
The present inventors have intensively studied to solve contamination immediately after coating as an object of coating obtained by mixing organolisilicate or a condensate thereof with an organic coating base. As a result, the present inventors have found that coating having very excellent anti-contamination effect immediately after coating is obtained by mixing a tetraalkoxysilane condensate (C1) or (C2), which is a condensate of a tetraalkoxysilane with a combination of a short-chain alkyl group and a long-chain alkyl group in place of the alkyl group, not a tetraalkoxysilane or a simple condensate thereof, with coating. Thus, the present invention has been accomplished.
The present invention is composed of a combination of the following resins and additives.
(1) A composition which is mainly composed of a combination of a polyurethane-forming component (PU-I) and (C1).
(2) A composition which is mainly composed of a combination of a polyurethane-forming component (PU-II) and (C2). This composition is characterized in that a weak solvent can be used, particularly.
(3) A composition which is composed of a combination of a polyurethane-forming component (PU-III) and (C1) and polycaprolactone diol and/or polycaprolactone polyol as an essential component. This composition forms a coat having elasticity, particularly.
(4) A composition which is mainly composed of a combination of an acrylic copolymer resin (AC) and (C1).
(5) A composition which is mainly composed of a combination of an alkoxysilyl group-containing acrylic copolymer resin (AS) and (C1).
The present invention will be described in detail hereinafter.
The anti-contamination coat composition of the present invention comprises a polyol compound (A1), a polyisocyanate compound (B1) and a tetraalkoxysilane condensate (hereinafter referred to as an xe2x80x9calkoxysilane condensatexe2x80x9d or an xe2x80x9calkyl silicate condensatexe2x80x9d, sometimes), wherein the polyol compound and polyisocyanate compound are contained in a ratio of 0.6 to 1.4 in terms of a NCO/OH ratio and the tetraalkoxysilane condensate is contained in the amount of 1.0 to 40.0 parts by weight in term of SiO2 relative to 100 parts by weight of the content of the polyol compound, and wherein the polyol compound (A1) has a weight-average molecular weight of 5000 to 80000 and a hydroxyl group value of 20 to 150 (KOH mg/g) and the tetraalkoxysilane condensate is a tetraalkoxysilane condensate (C1), which has an average condensation degree of 4 to 20 and has an alkyl group having 1 to 2 carbon atoms and an alkyl group having 3 to 10 carbon atoms, the alkyl group having 3 to 10 carbon atoms being contained in the amount of 5 to 50% by equivalent based on all alkyl groups in the condensate.
By adopting such a construction, there can be obtained a coating, which is extremely superior in effect of preventing contamination immediately after coating to the case where a hydrophilic alkoxysilane compound alone or its condensate is added, and which has a soil-release effect and is also superior in stain resistance to oily contamination, weathering resistance and other coat physical properties.
When the molecular weight of the above polyol is smaller than 5000, the curing property and durability of the coat are not sufficient. On the other hand, when the molecular weight is larger than 80000, the finishing property of the coat is not sufficient. Considering the change of the other raw materials, the molecular weight is preferably within the range from 20000 to 60000 because the coat having stable characteristics is formed.
When the hydroxyl group value is less than 20 KOH mg/g, the durability and contamination resistance of the coat are poor. On the other hand, when the hydroxyl group value exceeds 150 KOH mg/g, the durability and flexibility of the coat are insufficient. When the hydroxyl group value is within the range from 30 to 100 KOH mg/g, particularly excellent characteristics can be obtained.
The glass transition point of these polyols is from xe2x88x9210 to 150xc2x0 C., preferably from 10 to 100xc2x0 C. When the glass transition point is lower than xe2x88x9210xc2x0 C., the contamination removing property and contamination recovering property are poor. On the other hand, when the glass transition point is higher than 150xc2x0 C., the flexibility and durability are poor.
It is considered that, in the present invention, when an alkyl group having 1 to 2 carbon atoms and an alkyl group having 3 to 10 carbon atoms coexist in the tetraalkoxysilane condensate, an anti-contamination coat having excellent surface orientation property and excellent coat physical properties can be formed.
The above tetraalkoxysilane condensate (C1) is contained in the amount of 1.0 to 40.0 parts by weight, preferably from 2.0 to 30.0 parts by weight, in terms of SiO2 relative to 100 parts by weight of the resin solid content of the polyol (A1).
When the amount is smaller than 1.0 parts by weight, the hydrophilicity is not sufficient and, therefore, the contamination resistance is poor. On the other hand, when the amount exceeds 40.0 parts by weight, problems such as poor appearance of the cured coat, crack and the like arise. When the amount is from 2.0 to 30.0 parts by weight, the influence of the material composition is hardly exerted and, therefore, stable characteristics can be obtained.
The hydrophilic alkoxysilane compound (D) containing an alkylene oxide chain can be added to the anti-contamination coating composition of the present invention. Because the hydrophilicity is further imparted to the coat by using in combination with the alkoxysilane condensate (C1), an excellent effect of preventing contamination can be obtained. By using it in combination, there can be obtained an anti-contamination coating composition which is particularly superior in stain resistance of the coat.
The present invention is also directed to an anti-contamination coating composition, wherein the above polyol compound (A1) is a solvent-soluble fluorine-containing copolymer obtained by copolymerizing a fluoroolefin, at least one of a vinyl ester and a vinyl ether, and a hydroxyl group-containing monomer as an essential constituent monomer.
By using a polyol containing fluorine as a polyol component constituting a polyurethane which is a resin component of coating, the long-term weathering resistance and effect of preventing contamination can be further improved.
In the coating composition of the present invention, it is a particularly preferable aspect to add the hydrophilic alkoxysilane compound (D) having a weight-average molecular weight of 150 to 3500 and containing an alkylene oxide chain having repeating units of 2 to 40 in the amount of 0.1 to 20 parts by weight relative to 100 parts by weight of the above polyol compound (A1).
Use of hydrophilic alkoxysilane compound (D) having a hydrophilic polyalkylene oxide chain further enhances the hydrophilicity of the coat immediately after coating thereby to effectively prevent the initial contamination.
As the component of anti-contamination coating of the present invention, an amine compound (E) is also preferably added in amount of 0.02 to 5.0 parts by weight relative to 100 parts by weight of the polyol compound (A1). By using such an amine compound, in addition to the above anti-contamination effect, the recoating property is also improved, and blister caused with a lapse of time in case of multi-layer coating, crack and lifting in case of coating two or more layers can be prevented effectively and, at the same time stiff coat can be formed. Therefore, there can be obtained an anti-contamination coat which is remarkably superior in durability.
In spite of the above amine compound, the compound having a tertiary amino group may be used as a polyol component. The anti-contamination coating composition according to the present invention is characterized in that the polyol compound contains a tertiary amino group-containing acrylpolyol, or the invention relates to the anti-contamination coating composition of the present invention, characterized in that the fluorine-containing copolymer contains a fluorine-containing copolymer having a tertiary amino group. By using such a polyol, the same effect as that obtained by adding an amine compound can be obtained.
The present inventors have intensively studied. As a result, they found that, in the case of the urethane resin coating using a polyol having solubility parameter SP of 6.5 to 9.5, which can be dissolved and/or dispersed in a solvent having particularly weak dissolving force, the coating surface can be hydrophilized by mixing the tetraalkoxysilane low condensate having a specific structure in the coating, thereby making it possible to provide a coat having good contamination resistance. Thus, the present invention has been completed.
The present invention further relates to an anti-contamination coating composition comprising a polyol compound (A2) having a solubility parameter SP of 6.5 to 9.5, a weight-average molecular weight of 5000 to 150000 and a hydroxyl group value of 15 to 100 (KOH mg/g) dissolved and/or dispersed in a non-aqueous solvent, a polyisocyanate compound (B2) in a NCO/OH equivalent ratio of 0.7 to 2.0, a tetraalkoxysilane condensate (C2) which is a condensate of tetraalkoxysilane having an average condensation degree of 4 to 10 and which has an alkyl group having 1 to 3 carbon atoms and an alkyl group having 4 to 12 carbon atoms, the alkyl group having 4 to 12 carbon atoms being contained in the amount of 5 to 50% by equivalent based on all alkyl groups in the condensate, and a hydrophilic alkoxysilane compound (D) having a weight-average molecular weight of 150 to 3500 and containing an alkylene oxide chain having repeating units of 2 to 40, wherein the tetraalkoxysilane condensate (C2) is contained in the amount of 1.0 to 50.0 parts by weight in term of SiO2 and the hydrophilic alkoxysilane compound (D) is contained in the solid content of 1.0 to 20 parts by weight, respectively, relative to 100 parts by weight of the resin solid content of the polyol compound (A2).
The present invention is further characterized by using the same PU-II base as described above, and containing 1.0 to 50.0 parts by weight of tetraalkoxysilane condensate (C2) and an amine compound (E) in the solid content of 0.02 to 5.0 parts by weight, respectively, relative to 100 parts by weight of resin solid content of polyol compound (A2).
When the weight-average molecular weight of A2 is smaller than 5000, a suitable viscosity as the coating is not obtained so that respective physical properties of the coat are poor. On the other hand, when it is larger than 150000, the sharpness and gloss of the coat are lowered, unfavorably. When the hydroxyl group value is smaller than 15 KOH mg/g, the crosslink density is low so that various physical properties and contamination resistance of the coat are poor. On the other hand, when it is larger than 100 KOH mg/g, the crosslink density becomes higher and, therefore, the durability and flexibility of the coat are insufficient and, at the same time, the surface orientation property of the tetraalkoxysilane condensate (C2) is inhibited, unfavorably.
As the component (A2), those having SP of 6.5 to 9.5 are used. By using those having such SP, it is possible to be dissolved and/or dispersed in a solvent having a weak dissolving force referred to as a weak solvent, thereby to prepare a weak solvent type coating. As a matter of course, it is possible to use after dissolving in a strong solvent having a strong dissolving force.
In the urethane resin coating using such a polyol compound (A2), a normal alkyl silicate has poor compatibility and poor surface orientation property so that the coat is contaminated. To the contrary, according to the present invention, the compatibility is good and surface orientation property is excellent and coat is hydrophilized so that a coat having excellent anti-contamination property can be provided. Furthermore, it is able to provide a coating composition having excellent various coat performances.
Furthermore, by adding a hydrophilic alkoxysilane compound (D), the surface of the coat is hydrophilized in the initial stage so that it is possible to provide an anti-contamination coating composition which is superior in contamination resistance and stain resistance.
It is also preferred to provide a composition obtained by adding an amine compound (E). When an anti-contamination coating composition is multi-coated, an effect that interlaminar adhesion becomes good is also exerted.
In the present coating compositions, it is suitable that an aliphatic hydrocarbon is contained in the amount of 50% by weight or more based on the whole solvents in the coating compositions. Therefore, lifting does not take place, thereby making it suitable for repair and an influence on the environment can be reduced.
The anti-contamination coating composition of the present invention may further contain a polyurethane-forming component (PU-III) wherein the polyol compound (A1) is a polyol compound having a glass transition temperature (Tg) of 15 to 100xc2x0 C. and the polyisocyanate compound (B1) has a concentration of a polyisocyanate group of the solid content of from 3 to 15% by weight, and a polycaprolactone diol and/or polycaprolactone triol (G) having a weight-average molecular weight of 300 to 3000 and a hydroxyl group value of 30 to 550 KOH mg/g are contained in the amount of 1 to 20 parts by weight relative to 100 parts by weight of the solid content of the polyol compound (A1).
In the present invention, the Tg of the polyol compound (A1) is limited. In the case of the coat having the flexibility, when Tg is lower than 15xc2x0 C., contaminants physically adhere and the contamination resistance is poor, and the weathering resistance is also deteriorated. On the other hand, when it is higher than 100xc2x0 C., the crack-following property of the undercoat disappears, resulting in poor waterproofing property.
As the polyisocyanate compound (B1), those having a NCO content of 3 to 15%, and more preferably 8 to 12%, based on the solid content of 100% are used.
When the NCO content is less than 3%, it is necessary to mix a large amount of a polyisocyanate compound, resulting in poor durability of the coat, unfavorably. On the other hand, when the NCO content is more than 15%, the coat becomes too hard and, therefore, the expected elastic coat can not be formed and the waterproofing performance is not obtained.
With regard to the component of polycaprolactone diol and/or polycaprolactone triol (G), when the weight-average molecular weight is less than 300, it is not preferable because of insufficient flexibility of the coat. On the other hand, when it is more than 3000, it is not preferable because finishing feel and workability are not satisfactory.
When the amount of such a component (G) is less than 1 part by weight relative to 100 parts by weight of the solid content of the component (A1), the flexibility of the coat is insufficient, unfavorably. When the amount exceeds 20 parts by weight, the weathering resistance of the coat is lowered.
The tetraalkoxysilane condensate component (C1) having a specific structure, wherein alkyl groups having 1 to 2 carbon atoms and those having 3 to 10 carbon atoms coexist, exerts the above effect, thereby obtaining a coating composition capable of forming an anti-contamination coat, which is superior in elasticity and physical properties of the coat. The invention further describes the anti-contamination coating composition wherein a hydrophilic alkoxysilane compound (D) having a weight-average molecular weight of 150 to 3500 and containing an alkylene oxide chain having repeating units of 2 to 40 was added in the amount of 0.1 to 20 parts by weight relative to 100 parts by weight of the solid content of the polyol compound (A1).
As described above, the anti-contamination performance immediately after formation of the coat is remarkably improved.
The present invention is further directed to an anti-contamination coating composition comprising a tetraalkoxysilane condensate (C1) in the amount of 1 to 30 parts by weight in terms of SiO2 relative to 100 parts by weight of the solid content of an acrylic copolymer resin (AC) which contains an acrylate and/or a methacrylate monomer and has a glass transition temperature of 0 to 100xc2x0 C.
By adopting the above construction, the surface is hydrophilized immediately after formation of the coat and the stain resistance is also excellent. Therefore, there can be obtained an anti-contamination acrylate resin coating composition, which exerts a soil-release effect of wash out contaminants and has good physical properties of the coat.
The anti-contamination coating composition of the present invention further comprises the hydrophilic alkoxysilane compound (D) having a weight-average molecular weight of 150 to 3500 and containing an alkylene oxide chain having repeating units of 2 to 40 in the solid content of 0.1 to 20 parts by weight.
By adding a hydrophilic alkoxysilane compound (D), the anti-contamination type acrylate resin coating composition having better anti-contamination performance in the initial stage can be obtained.
The present invention further relates to an anti-contamination coating composition comprising a compound (C1) which is a tetraalkoxysilane condensate having an average condensation degree of 4 to 20 and which has an alkyl group having 1 to 2 carbon atoms and an alkyl group having 3 to 10 carbon atoms, the alkyl group having 3 to 10 carbon atoms being contained in the amount of 5 to 50% by equivalent based on all alkyl groups in the condensate, in the amount of 1.0 to 20.0 parts by weight, and more preferably 1.0 to 10 parts by weight, in terms of SiO2 relative to 100 parts by weight of the solid content of an alkoxysilyl group-containing acrylic copolymer resin (AS) which has a group represented by the general formula 
wherein R1 represents an alkyl group having 1 to 10 carbon atoms; R2 represents a hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of alkyl, aryl and aralkyl groups having 1 to 10 carbon atoms; and a represents 0, 1 or 2.
The characteristics of the present invention are as follows. That is, since the anti-contamination performance obtained immediately after formation of the coat is better than that of an anti-contamination coating composition containing a conventional alkoxysilyl group-containing acrylic copolymer resin and a tetraalkoxysilane, and the anti-contamination can be obtained by smaller concentration of the alkoxysilyl groups and smaller amount of the tetraalkoxysilane compound in comparison with the prior art, an anti-contamination coating composition, which is advantageous in view of the performance of the coat and cost, can be obtained. In the portion of the alkyl group of the compound (C1), alkyl groups having 1 to 2 carbon atoms and alkyl groups having 3 to 10 carbon atoms coexist so that the compatibility with the component (AS) is remarkably improved similar to the other case, thereby making it possible to form an anti-contamination coating composition which is superior in surface orientation property and physical properties of the coat.
To the anti-contamination coating composition of the present invention, it is preferable to further add the hydrophilic alkoxysilane compound having a weight-average molecular weight of 150 to 3500 and containing an alkylene oxide chain having repeating units of 2 to 40 in the solid content of 0.1 to 20 parts by weight.
Similar to the above case, when the amount of the compound is less than 0.1, sufficient addition effect can not be obtained. When it exceeds 20, the compatibility with the resin component and water resistance of the cured coat are not sufficient.
As described above, the present invention is characterized by using an alkoxysilane condensate (C1) or (C2), the substituted alkyl group varies depending on (C1) or (C2) and its preferable maximal addition amount varies. This is because the compatibility and physical properties imparted to the cured coat vary depending on the objective resin component. The optimum combination and the optimum addition amount are decided according to the resin on the basis of the test.
It is particularly preferred that the alkylene oxide chain of the above hydrophilic alkoxysilane compound (D) is an ethylene oxide chain because high hydrophilicity can be obtained.